Define Region(s) in Childwindows using Prism + MVVM

I am using Prism + MVVM to Inject views in regions. I use several Childwindows using Interaction requests, but I am unable to define Regions in these Childwindows. The RegionManager isn't avaibale/accesible in the xaml and xaml.cs files. With Interaction
requests, I can't add parameters in the constructor, to pass the RegionManager.

From the View that shows the Childwindow, we call the following Interaction request from the ViewModel:

In the previous code snippet, a new RegionManager is obtained through the
Service Locator, however you might need to use an existing
RegionManager or to create a new one and access it outside your
PopupView. For doing this you could, for example, use a shared service (e.g. an object registered as a singleton in the container) to pass the
RegionManager to/from the PopupView and obtain the shared service through the
Service Locator. However, the specific details of how to implement this depends mostly of your personal preferences and the requirements of your scenario.

As a side note, if you use the view discovery approach (for example, registering a view in a region with the
RegisterViewWithRegion method) it's not required for the view containing the region (in this case the
PopupView) to have a RegionManager attached.

Also, in case you require a PopupChildWindowAction with a custom behavior (like for example, accepting parameters for the view) you might find the following thread useful where you can find an example of a custom
PopupChildWindowAction: